1. Field of the Invention
The present invention relates to a solid-state imaging device, a camera module and a manufacturing method for the camera module, wherein a thickness in an optical-axis direction is thin and it is possible to assemble the solid-state imaging device and an optical unit with great accuracy.
2. Description of the Related Art
A digital camera and a video camera employing a solid-state imaging device are widely used. Further, it is also done to add a photographing function to a personal computer and electronic equipments of a cellular phone, an electronic notebook and so forth by incorporating the solid-state imaging device and amemory therein. In order to easily add the photographing function to the electronic equipments except the digital camera, is provided a unitized camera module in which the solid-state imaging device, an optical unit and a circuit board are assembled in advance. The optical unit has a built-in imaging optical system, and the circuit board is provided with a control circuit.
The solid-state imaging device comprises a light-receiving element and an external connection terminal, which are formed on a semiconductor substrate made from silicon. In case the solid-state imaging device is in a state that the light-receiving element is not protected, namely in case the solid-state imaging device is a bare chip, dust and dart adhere to the light-receiving element and a trouble is caused. Therefore, in the conventional solid-state imaging device, the bare chip is contained in a package formed from ceramic and so forth. The solid-state imaging device and the package are connected by wire bonding. A cover glass is attached to an opening of the package to supply the solid-state imaging device in a sealed state.
As to one of mounting manners for downsizing the solid-state imaging device, there is a chip-size package (hereinafter, abbreviated as CSP) structure wherein mounting the solid-state imaging device is completed without using the package (see U.S. Pat. No. 7,074,638). The solid-state imaging device of the CSP type is provided with a spacer, which is disposed on an upper surface of the semiconductor substrate so as to surround the light-receiving element. A cover glass is attached to the top of the spacer to seal the light-receiving element.
In order to obtain a high-quality photographic picture by effectively utilizing performance of the solid-state imaging device, it is necessary to make a photographic optical axis of the imaging optical system coincide with the center of a light-receiving area of the solid-state imaging device. Further, it is also necessary to make the light-receiving element of the solid-state imaging device perpendicular to the photographic optical axis of the imaging optical system. If the photographic optical axis of the imaging optical system does not coincide with the center of the light-receiving area of the solid-state imaging device, shading and so forth occur due to a decline of a light amount, deterioration of resolution, and unevenness of sensitivity. Moreover, if the solid-state imaging device inclines relative to the photographic optical axis, it is impossible to obtain a proper image due to a condition of so-called “swing-and-tilt photographing”.
In a conventional way, image pickup is performed with the solid-state imaging device during an assembly operation for the purpose of assembling the solid-state imaging device and the optical unit with great accuracy. A pickup image is viewed to carry out an operation (aligning operation) for deciding relative positions of the solid-state imaging device and the imaging optical system. The aligning operation, however, takes a lot of time so that it is caused to increase the cost and to deteriorate a yield rate.
In order to accurately assemble the solid-state imaging device and the optical unit without the above-mentioned aligning operation, a plurality of positioning plates are attached to the outside of the package of the solid-state imaging device described in Japanese Patent Laid-Open Publication No. 05-102448. By using the positioning plates, the solid-state imaging device is positioned and fixed to the optical unit. Meanwhile, with respect to the solid-state imaging device described in Japanese Patent Laid-Open Publication No. 11-252416, an attachment reference plane is accurately formed on the package. The attachment reference plane abuts on a reference plane of the optical unit to carry out positioning and fixing.
As to the solid-state imaging device sealed in the package, positioning accuracy thereof relative to the optical unit is affected by size accuracy of the package, assembly accuracy of the solid-state imaging device and the package, and assembly accuracy of the package and the optical unit. Therefore, even if the package is attached to the optical unit with great accuracy, positional accuracy of the solid-state imaging device and the optical unit is not greatly improved. The aligning operation is still required to carry out appropriate positioning.
The solid-state imaging device sealed in the package has a broad external size (project area perpendicular to an optical-axis direction) and a wide size in the optical-axis direction (thickness size). Thus, the digital camera and the camera module, in which the solid-state imaging device is incorporated, are prevented from being downsized.